With WWE trying so hard to get Roman Reigns over as a credible babyface, utilizing John Cena as Reigns' opponent in 2016 would definitely help their cause. The marquee of that match alone seems fit for a WrestleMania main event, but like with The Undertaker, it's far from certain that this match will happen in Dallas. Unlike The Undertaker, Cena isn't going anywhere anytime soon which means that a feud with Reigns is inevitable. Any rivalry between Reigns and Cena should be something that is built towards slowly and should culminate at a big-time show. The only big-time shows that seem to exist with any regularity in WWE anymore are WrestleMania and SummerSlam. Just because it should headline one of these events, doesn't mean it will as WWE has a history of booking high profile matches on seemingly second-rate PPVs (e.g. FastLane 2015, Battleground 2015, Hell In A Cell 2015). The sooner WWE pulls the trigger though, the better the chances are that the fans will rally behind Roman instead of Cena. This makes a match between the two in 2016 a possibility.